Along with rapid development of computer networks, more stringent time synchronization has been required in an increasing number of industrial fields, and time synchronization at a sub-microsecond level has been required especially in the majority of industrial Ethernet-based distributed control systems. Particularly, in a smart substation automation system and distributed control system, higher time uniformity may be required in view of real-time data collection, scheduling and control.
A precision synchronization clock protocol relating to network communication, local computation and object allocation in a test and control network has been defined in the IEEE-1588 Precision Time Protocol (PTP). This protocol supporting system-wide time synchronization can be applicable to both a wide area Ethernet and a multipoint transmission-enabled local area network and can achieve the time synchronization precision at a sub-microsecond level. The IEEE-1588 precision time synchronization algorithm has been widely applied in power supply management, industrial control, test and measurement, network communication and other fields due to its high synchronization precision, low-cost implementation, convenience to deploy and maintain and other superiorities.
The currently used PTP version is generally the IEEE1588V2 version with an additional support of a transparent clock comparing to the V1 version to thereby further alleviate the difficulty to implement IEEE1588 and improve the stability and the time synchronization precision of IEEE1588, and particularly for the network node run on transparent clock protocol (that is transparent clock node), it is more appropriate to transport the clock information in a switch system.
During existing network deployment, if a complex topology network or a loop network is deployed across a plurality of transparent clock nodes, then a transparent clock node performs only frequency synchronization upon a received PTP packet without phase synchronization, and a transparent clock node forwards the PTP packet simply after performing tome process on the received PTP packet, so there may be a protocol storm in the loop network due to the PTP packets and consequently time synchronization cannot be performed in the network.
In the prior art, there is such a solution to this problem that whether to forward a PTP packet is determined by a port status of a spanning tree, and this solution can address the problem of transparent time synchronization in a network with a spanning tree, but a device, for which there are a plurality of spanning trees and a network is deployed with routing, can not judge, or can not judge purely, from the status of a port spanning tree, whether to forward a transparent clock packet and consequently the PTP may fail.